Conventional data transmission in line-switched narrowband telecommunications networks is based on analog and digitized data transmission at a data transmission rate of 64 kbit/s or fractions thereof. At this data transmission rate, voice, data such as texts or images can be transmitted in a telecommunications network whose digital design and signaling are known by the term Integrated Services Digital Network ISDN.
With the dawn of the multimedia age, the demand for data volumes to be transmitted has risen sharply, with the result that the aforementioned data transmission rate is no longer adequate for these applications. Applications such as access to online services, e.g. the Intranet or Internet, videoconferencing, distance learning, telemedicine, high-bit-rate data transmission, etc., require data transmission rates amounting to a multiple of the data transmission rate of an ordinary telephone call. The aforementioned applications may be allocated to one of the following three classes: narrowband up to 64 kbit/s, wideband over 64 kbit/s to 2 Mbit/s, and broadband over 2 Mbit/s.
Whereas broadband networks, with their high data transmission rates, require an overlay network separated from the narrowband network and designed, for example, on the basis of Asynchronous Transfer Mode ATM technology, this is uneconomical for wideband connections. For these data transmission rates, a method is therefore used which is known by the term channel bundling. In channel bundling, data at the transmitting end are split up into data streams with a granularity of 64 kbit/s and are switched through the network via individual channels. According to the definition of wideband connections, between 2 and 30 channels are required for this purpose. At the receiving end, the data from these N channels must in turn be recombined as they were transmitted from the transmitting end. To do this, the temporal and logical association of the data on the N channels must be known to the receiving end.
In a network with digitally transmitted data, each connection comprises consecutive segments which are formed by exchanges and transmission segments. Switching through an exchange can be effected here by entering dialing information, or administratively using a dedicated connection. Data can be transmitted via a multiplicity of connection paths of different designs.
A distinctive feature of a line-based dial-up connection network is that each connection is switched through the dial-up connection network independently of all other connections. Optimum utilization of existing network resources determines the path of the individual connection through the network. The initiator of such a connection has little influence on this path. The network operator influences the routing of the data traffic streams by setting up control mechanisms.
In addition to the distribution of data traffic streams in a transmission network, the routing of data traffic streams within an exchange must be taken into consideration. In general, an individual exchange in turn comprises a combination of switching devices which are meshed with one another by means of corresponding data transmission channels.
On the whole, each line-switched connection can thus be represented within a switching network as a combination of at least two terminal devices, k switching units and k+1 data transmission paths.
A terminal-device-based solution variant and a network-based solution variant are available for identifying the association of transmitted data in wideband connections and for restoring the data in their transmission sequence. The network-based solution is examined more closely below.
Corresponding to a data transmission rate which is to be made available, N channels are set up as a single N-fold connection through the switching network. Within the switching network, the switching system ensures that the required N single channels are always routed together in one PCM system throughout the entire network, i.e. their temporal association is retained. When the N single channels are switched through within an exchange, it must furthermore be ensured that the logical sequence or logical association of the N single channels is not modified. The individual conditions to be observed for this purpose are summarized in guidelines for compliance with the sequence of the PCM time slots (Time Slot Sequence Integrity DSSI). As a result, along with special requirements for the switching networks of the exchanges, the N single channels of an Nx64 kbit/s connection between the exchanges and from/to the terminal devices must always be located in the same PCM system.
In order to comply with the above-mentioned conditions, the single channels of the N-fold connection must in each case be coordinated in the switching units and the switching procedures must be carried out for each channel. This has the disadvantage that the processors of the switching units are burdened with a multiplicity of coordination and N-fold switching procedures, during which they cannot be used for other switching tasks.
A through-connection of broadband channels comprising a plurality of single channels for time division multiplex systems with delta modulation is known from U.S. patent specification 4,512,014. Hold or voice storage addresses in each case of one single channel only are transferred by the central controller to a hold latch, while the addresses of the remaining sub-channels of the broadband signal are generated locally and independently under the influence of a corresponding identifier with the aid of the time-slot counter for cyclical activation of the hold latch.
The object of the invention is to indicate a circuit arrangement and a method for joint switching through of at least two single channels in one switching unit, avoiding the above-mentioned disadvantages.
The object is achieved by means of the features of claims 1 and 7.
The invention offers the advantage that no coordination of N single channels is required in a switching device.
The invention offers the advantage that all switching activities such as digit evaluation and processing, routing, network features, barring evaluation and charging are required for one channel only, i.e. once for each switching-through of the entire connection.
The invention offers the advantage that adherence to the sequence of PCM time slots during switching through the switching devices of the switching system can be effected without major outlay, since all N paths can in each case be handled with one N-fold setting command.
The invention offers the advantage that faults need only be cleared from one main connection.
Further special features are indicated in the subclaims.